Constant monitoring is underway across New Jersey's 21 counties to ensure the mosquito population doesn't get out of hand and cause a public safety concern.

When necessary, officials are spot-treating areas where the presence of the bloodsucking insects is unbearable, or where an overwhelming presence of larvae can be eliminated.

No human cases have been reported yet, but the latest report from the state Department of Health confirms that mosquito samples have tested positive for West Nile virus in 13 New Jersey counties — Atlantic, Bergen, Burlington, Camden, Cape May, Gloucester, Hunterdon, Mercer, Monmouth, Ocean, Salem, Somerset and Warren.

In total, 35 mosquito pools tested positive for the virus through July 7.

According to Tadhgh Rainey, manager of the Hunterdon County Division of Health, positive West Nile readings are not unusual for this time of year.

Rainey said the county was seeing "tremendous numbers" of mosquitoes earlier in the season, but those numbers are starting to fade.

"We're certainly not seeing what we see a month ago," he said.

This time last year, just 25 pools in nine counties tested positive for West Nile.

Over 3,000 sites are documented in Monmouth County as potential breeding grounds for mosquitoes. But the true number grows with every instance of standing water, including ornamental ponds and planter saucers on your property.

"If there's some water, there is a mosquito that will take advantage of it," said Vicki Thompson, superintendent of Monmouth County Mosquito Control.

If granted permission, the division will go on private property to treat areas, Thompson said.

Like Hunterdon, Monmouth County has seen a recent decrease in mosquito activity, following a "strong start" to the season.

"The spring was incredibly wet," Thompson said. "We had over five inches more than average of rainfall from April to June 1st."

Mosquito monitoring starts in February or March, Thompson said. Treatment — through spraying and other methods — begins as the weather warms up, and continues throughout the summer as necessary.

By law, agencies must notify the public when they intend to use a spray treatment to kill mosquitoes in the area.

Dozens of sites across a handful of municipalities were scheduled for a spraying Thursday and Friday in Camden County.

“The commission works with the Public Health Environmental Laboratories in Trenton to verify the presence of West Nile virus and other communicable diseases in their samples,” Freeholder Jeff Nash, liaison to the Camden County Mosquito Commission, said in a news release. “If a pool tests positive, the Mosquito Commission returns to spray the area. The sprayings take place when the mosquitoes are most active.”

The spray used by counties is not harmful to humans or pets, but individuals with respiratory concerns or a sensitivity to irritants are advised to avoid direct contact.

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Contact reporter Dino Flammia at dino.flammia@townsquaremedia.com.